Security devices

ABSTRACT

Relay contacts are controlled by obtaining zero output simultaneously from two or more balanced circuits. Such simultaneous balance signifies that a corresponding number of resistance values in a &#39;&#39;&#39;&#39;key&#39;&#39;&#39;&#39; device complement the resistance values in a &#39;&#39;&#39;&#39;combination&#39;&#39;&#39;&#39; device which is formed as a plug for ready changing of the combination by the substitution of a different plug. The number of combinations obtained increases as the power of the number of balanced circuits. The relay contacts can be used to control a lock, burglar alarm or other security device.

United States Patent Saul [54] SECURITY DEVICES [72] Inventor: Benno Bensiyon Saul, 5830 St. Luc, Apt.

16, Montreal, Quebec, Canada [22] Filed: June 10,1970 [21] Appl.No.: 45,064

[52] US. Cl ..307/235, 340/280, 340/285 [51 Int. Cl ..H03k 5/00, G08b 21/00 [58] Field of Search ..340/274, 280, 285; 307/235 [56] References Cited UNITED STATES PATENTS 3,407,400 lO/ 1968 Lurie ..340/280 3,425,050 l/l969 Tellerman et a] ....340/280 X 3,439,359 4/ 1969 Sliman ..340/285 X [151 3,656,001 [4 1 Apr. 11,1972

3,537,095 10/1970 Cones ..340/280 Primary Examiner-John Zazworsky Attorney-Peter Kirby, Charles P. Curphey and Norris M. Eades [57] ABSTRACT Relay contacts are controlled by obtaining zero output simultaneously from two or more balanced circuits. Such simultaneous balance signifies that a corresponding number of resistance values in a key device complement the resistance values in a combination" device which is-formed as a plug for ready changing of the combination by the substitution of a different plug. The number of combinations obtained increases as the power of the number of balanced circuits. The relay contacts can be used to control a lock, burglar alarm or other security device.

1 Claims, 4 Drawing Figures Patented April 11, 1972 2 Sheets-Sheet 1 Patented April 11, 1972 2 Sheets-Sheet 2 SECURITY onvrcss This invention relates to an electrically operated security device, e.g. a lock or alarm device of the type that requires use of a special key having a predetermined electrical value to operate it. The invention has for its primary object an improvement in such devices, that permits quick and convenient changing of the combination, as well as the provision of a large number of such combinations without undue complexity or duplication of the equipment.

One application of the invention is to the improvement of burglar alarm systems. Other applications are to the enhancement of the security of any other devices that are normally closed by an electrically operated lock, for example the access door of a typical vending machine.

In the present inventors U.S. Pat. No. 3,5l8,655 issued June 30, 1970 there is disclosed a system using a so-called balanced circuit (abridge circuit) including a pair of electrically matched resistance elements for balancing the circuit. One of these elements is so made as to be readily removable from the system, for replacement by a different but similar element. For example, this element may be mounted on a plug representing a specific combination" by virtue of the electrical resistance of the resistor element connected between the prongs of the plug. In this way, by removing one plug from the system and inserting another with a different electrical resistance, the combination can be rapidly and readily changed. The second of the matched elements is then formed as a key which also consists of an electrical resistance that can be introduced into the system from some appropriate external point. For each plug element there will be only one correct key for balancing the bridge circuit. The latter will then act in combination with an electrical lock or other security system to release the same.

Theoretically the number of combinations of resistance values in such a system is infinite, but, in practice, it is restricted by the commercially available resistors and the tolerances that must be adopted. A reasonable spacing must be provided between the chosen resistance values.

The principle object of the present invention is to provide an improvement in this type of system in which a greatly increased number of combinations is obtainable, while at the same time the equipment is not unduly complicated or multiplied.

The various features of the invention will become more readily apparent with the aid of the circuits illustrated in the accompanying drawings. It is to be understood that these circuits are provided by way of example only, and not by way of limitation of the broad concepts of the invention, which latter are defined in the appended claims.

In the drawings:

.FIG. 1 is a simplified circuit illustrating the principle of the present invention;

FIG. 2 is a circuit of a first embodiment of the invention;

FIG. 3 is an equivalent circuit of part of FIG. 3; and

FIG. 4 is a fragmentary circuit illustrating a modification.

Referring firstly to FIG. 1, power is supplied from a transformer T to a pair of balanced circuits consisting of resistors R1, R2 and R3, R4. When the resistance value of resistor R1 equals that of resistor R2, the point M is at ground potential. Similarly, when the resistance value of the resistor R3 equals that of resistor R4 the point N is also at ground potential.

A diode D1 is connected to provide a half wave rectified positive voltage gradient along a resistor R5, a selected level of which is transferred from a movable tap through a resistor R6 to a control point C. The control point C is connected to the gate of operating means in the form of a silicon controlled rectifier SCR (or other solid state switch) which remains switched off as long as the control voltage at the point C is negative. The anode of the rectifier SCR is connected through a relay R to one side of the transformer secondary, with a capacitor C1 connected across the relay for smoothing purposes.

through a diode D2,

Each of points M and N is connected to the control point C D3, respectively, and a resistor R7. If either of the balanced circuits is unbalanced, i.e. R1 is not equal to R2 or R3 is not equal to R4, then an alternating voltage will appear at the point M or N, respectively, and the negative halves of such voltage will be transmitted through the respective diode D2 or D3 to the point C to maintain the same negative and the rectifier SCR shut ofi. Only when both pairs of resistors are balanced, so that there is no voltage at either point M or N, will the voltage at the control point G be determined by the positive voltage derived from the resistor R5. The rectifier SCR is then switched on and the relay R energized to close its contacts. The capacitor C2is provided for. smoothing the alternating current rectified by the diodes D2, D3, and the Zener diode Z is provided to limit the voltage that can appear at the point C.

Thus this circuit constitutes detecting means that operates the relay R when it detects the condition that both so-called balanced" circuits are in fact simultaneously balanced. The resistors R2 and R4 can be formed in a key, while the resistors R1 and R3 can be mounted in a combination" plug for insertion in the system, so that the combination can be changed to require a difierent key for balancing the system. Assuming that, as a practical matter, there are 50 different values that can be given to each of the resistors R1 and R2, and a similar number of possible different values for the resistors R3 and R4, then the total number of combinations becomes 2,500. By adding a third resistance pair to the system, the total number of combinations is increased to the third power of the basic number of different resistance values usable. As will be apparent, a fourth resistance pair raises the total number of combinations to the fourth power of the basic number of different resistance values, and so on. The greatly increased number of combinations achieved in this way can be utilised, if desired, to reduce the number of different resistance values used, e.g. from 50 to 25, while still retaining an adequate number of total combinations. This facility has the advantage that a smaller number of resistance values enables such values to be spaced apart more from each other, which in turn permits greater tolerances in the other components and the use of less sensitive circuit components generally.

As above mentioned the relay contacts can simply be used to open or permit the opening of a lock. Alternatively, they can be used in an alarm system, such as the burglar alarm described in said patent No. 3,518,655. In this case the relay contacts feed an input to an AND gate that receives another input from a series of door and/or window contacts, in the manner set out in FIG. 1 of such other application.

While FIG. 1 herein illustrates the broad principle of the present invention, a circuit showing a typical structural arrangement is provided by FIG. 2. This drawing shows a socket 40 having seven contacts 41, 42, 43, 44, 45, 46 and 47. A portable structure in the form of a plug or other removable member for insertion into the socket 40 is diagrammatically illustrated at 50, and has corresponding pins 51, 5 2, 53, 54, 55, 56 and 57. It will be noted that pins 52 and 53 are permanently interconnected and that resistors R10, R11, R12 and R13 are respectively connected between pins 55 and 56; 54 and 57; 55 and 51; and 54 and 51.

As in the circuit of FIG. 1, the transformer T supplies power to the relay R which is arranged in series with the rectifier SCR, the gate of which is still controlled by the voltage at control point C. A second transformer T2 supplies power to the diode D1 which acts in the same manner as in FIG. 1 to provide a positive potential at the tap of resistor R5.-

A key or other like removable member 60 contains three terminals 61, 62 and 63 for connection to three socket contacts 71, 72 and 73, respectively, when the key is inserted in a complementary socket assembly. Key terminals 61 and 62 are respectively connected to resistors R15 and R14, the far ends of which are common and are connected to the terminal 63.

A very high resistance R18 is connected between socket contacts 45 and 41, to be in parallel with the resistor R12 when the plug 50 is in place. This resistor provides sufficient unbalance in the system when the plug 50 is removed to ensure that there will then always be some alternating current at the point M.

Assuming that the plug 50 is in place in the socket 40, it will be seen that there is one resistance arm leading from one side of the transformer T2 through contact 41, pin 51, resistors R12 and R18 in parallel, pin 55, resistor R10, pin 56, contact 46, socket contact 72, terminal 62, resistor R14, terminal 63 and socket contact 73 to the other side of the transformer T2. This resistance arm is better appreciated from the illustration of FIG. 3, along with a similar resistance arm consisting of the resistors R13, R11 and R15. It will be notedthat the pins 54 and 55 engage the socket contacts 44 and 45 which constitute the points N and M respectively. Thus, each of these balanced circuits will in fact be balanced so that the points M and N will simultaneously have no potential on them, provided that the resistance values are as follows:

R12 and R18 in parallel R R14, and R13=R11 +Rl5.

As in the case of FIG. 1, the points N and M are connected through diodes D3 and D2 to the control point C, capacitors C3 and C4 being interposed for isolation. Resistors R16 and R17 are also provided for the discharge of these condensers as the points N and M approach balance. The Zener diode Z and condenser C2 act as before.

When no negative voltage is generated by one or other of these circuits, the control point C is held positive by means of a voltage tapped from the resistor R5 which receives the positive half cycles passing through the diode D1 by virtue of the interconnection of socket contacts 42 and 43 through the plug pins 52 and 53.

FIG. 4 shows a modification in which a more complex network can be'used to obtain both a larger number of combinations and addition security against the lock being "picked by an intending intruder who attempts to measure the resistance values appearing between the socket contacts 71, 72 and 73 as a result of the combination of resistors R10, R11, R12, R13 and R18 and to construct a complementary key accordingly. in this case, the key 60' again has three terminals, but these are now internally interconnected by a network of resistors R20, R21, R22, R23, and R24. The remainder of the apparatus will have fixedly mounted resistors R25 and R26, as well as resistors R27, R28, R29, R30 and R31 mounted on a plug 50'. It will be readily apparent that the points M and N will be at zero potential when the following resistance conditions pertain:

R20 R25 R27 R21 R26 R28 to break down in the event of one of these points having applied to it a voltage higher than a desired maximum. This arrangement prevents an attempt to damage the system to put it out of order by the application of high voltages from the exterior through the key socket contacts.

It will be appreciated that other impedance elements such as inductors or capacitors could be used instead of resistors in achieving the necessary balanced circuits, although in practice resistors will be the more convenient and economical to use.

I claim:

1. An electrically operated security device comprising:

a. a detecting circuit,

b. first and second sockets each having contacts connected to said detecting circuit,

c. a plurality of first plug devices each for engaging in said first socket,

d. a plurality of second plug devices each for engaging in said second socket,

e. each of said first and second plug devices containing at least two impedance elements, the impedance values of the elements of each of said first plug devices being different from the impedance values of the elements of all other said first plug devices, and the impedance values of the elements of each of said second plug devices being different from the impedance values of the elements of all other said second plug devices,

f. said detecting circuit containing means for detecting a balanced condition between the impedance values of the elements of a selected first plug device engaged in said first socket and the impedance values of the elements of a selected second plug device engaged in said second socket, said balanced condition being such that at least two points in a network constituted by the at least four impedance elements of the selected first and second plug devices are simultaneously each at a predetermined voltage,

g. and operating means connected to said detecting circuit to react in a first manner to said balanced condition and in a second manner to the existence of a voltage at either of said points different from its predetermined voltage. 

1. An electrically operated security device comprising: a. a detecting circuit, b. first and second sockets each having contacts connected to said detecting circuit, c. a plurality of first plug devices each for engaging in said first socket, d. a plurality of second plug devices each for engaging in said second socket, e. each of said first and second plug devices containing at least two impedance elements, the impedance values of the elements of each of said first plug devices being different from the impedance values of the elements of all other said first plug devices, and the impedance values of the elements of each of said second plug devices being different from the impedance values of the elements of all other said second plug devices, f. said detecting circuit containing means for detecting a balanced condition between the impedance values of the elements of a selected first plug device engaged in said first socket and the impedance values of the elements of a selected second plug device engaged in said second socket, said balanced condition being such that at least two points in a network constituted by the at least four impedance elements of the selected first and second plug devices are simultaneously each at a predetermined voltage, g. and operating means connected to said detecting circuit to react in a first manner to said balanced condition and in a second manner to the existence of a voltage at either of said points different from its predetermined voltage. 